RAW to PNG issues with levels

Windows 10 in explorer loads the raw thumbnails as they where shot and look like the jpegs. However, when you open the png with gimp after the conversion, they show up incredibly dark, and the levels are shifted hard left. This isn't to much of an issue as you can drag the high point left back to center the histogram, but then all the colors (especially blue) get whacked and are often unrecoverable.